Methods and apparatus for maintaining a pressure within an environmentally controlled chamber

0001This patent application claims priority from U.S. Provisional Patent Application Ser. No. 60/211,402, filed Jun. 14, 2000, which is hereby incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

0002The present invention relates to vacuum technology and more particularly to methods and apparatus for maintaining a pressure within an environmentally controlled chamber such as a vacuum chamber.

BACKGROUND OF THE INVENTION

0003<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram of a conventional system <b>100</b> for maintaining a pressure within a transfer chamber <b>102</b> of a semiconductor device manufacturing tool (e.g., the Endura™ (shown in <figref idref="DRAWINGS">FIG. 4</figref>) or the Centura™, both manufactured by Applied Materials, Inc.). The transfer chamber <b>102</b> is shown coupled to a first load lock <b>104</b> and to a second load lock <b>106</b>. The load locks <b>104</b>, <b>106</b> are adapted to transfer semiconductor wafers to and/or from the transfer chamber <b>102</b> as is well known in the art.

0004With reference to <figref idref="DRAWINGS">FIG. 1</figref>, to employ the conventional system <b>100</b> to maintain a pressure within the transfer chamber <b>102</b>, a user (not shown) supplies a user defined input <b>108</b> to a mainframe controller <b>110</b> of the conventional system <b>100</b> (e.g., a conventional fabrication controller such as a manufacturing execution system (MES)). The user defined input <b>108</b> represents a pressure at which the transfer chamber <b>102</b> is to operate (e.g., a set point pressure for the transfer chamber <b>102</b>).

0005To maintain the set point pressure within the transfer chamber <b>102</b>, the conventional system <b>100</b> employs a mass flow controller <b>112</b> to adjust a flow rate of nitrogen (or some other inert, non-reactive gas supplied from a regulated gas supply <b>114</b>) into the transfer chamber <b>102</b> and employs a throttle valve <b>116</b> to adjust a rate at which the nitrogen (and any other impurities such as oxygen that are out-gassed from the chamber walls) is pumped from the transfer chamber <b>102</b> (via a vacuum pump <b>118</b>). Accordingly, after receiving the user defined input <b>108</b>, the mainframe controller <b>110</b> employs an algorithm to (1) calculate a flow rate of nitrogen into the transfer chamber <b>102</b> (e.g., by calculating a flow rate set point for the mass flow controller <b>112</b>); and (2) calculate a pump rate of nitrogen (and any other gases) from the transfer chamber <b>102</b> (e.g., by calculating a throttle valve position control signal for the throttle valve <b>116</b>). The flow rate set point and the throttle valve position control signal are provided from the mainframe controller <b>110</b> to the mass flow controller <b>112</b> and to the throttle valve <b>116</b>, respectively, as shown in FIG. <b>1</b>.

0006The mainframe controller <b>110</b> provides a pneumatic control signal to a first isolation valve <b>120</b> so as to open the first isolation valve <b>120</b> and allow nitrogen to flow from the regulated gas supply <b>114</b> through the mass flow controller <b>112</b> and into the transfer chamber <b>102</b> via a nitrogen filter <b>122</b> (e.g., a Millipore distributed by U.S. Filter, Inc.); and the mainframe controller <b>110</b> provides a pneumatic control signal to a second isolation valve <b>124</b> so as to open the second isolation valve <b>124</b> and allow the vacuum pump <b>118</b> to pump the transfer chamber <b>102</b>.

0007After establishing the flow rate of the mass flow controller <b>112</b> and the position of the throttle valve <b>116</b>, the mainframe controller <b>110</b> employs a first pressure transducer <b>126</b> (e.g., an MKS Instruments' capacitive manometer, a Baratron capacitive manometer, a Granville Philips' convection gauge, etc.) coupled to the transfer chamber <b>102</b> to monitor the pressure within the transfer chamber <b>102</b> (e.g., by periodically sampling the output signal of the first pressure transducer <b>126</b>). Based on each sampled output signal of the first pressure transducer <b>126</b>, the mainframe controller <b>110</b> recalculates a flow rate set point for the mass flow controller <b>112</b> and a throttle valve position control signal for the throttle valve <b>116</b> (to adjust the flow rate of nitrogen into the transfer chamber <b>102</b> and/or the pump rate of gas from transfer chamber <b>102</b>) so as to achieve the pressure originally defined by the user defined input <b>108</b>. Note that some conventional throttle valves may include a local controller for monitoring chamber pressure and adjusting throttle valve position based thereon.

0008When pressure variations result in the transfer chamber <b>102</b> (e.g., due to the opening of the first load lock <b>104</b> when a wafer is transferred into the transfer chamber <b>102</b> from the first load lock <b>104</b>, the opening of the second load lock <b>106</b> when a wafer is transferred out of the transfer chamber <b>102</b> to the second load lock <b>106</b>, and/or when a processing chamber (not shown) coupled to the transfer chamber <b>102</b> is opened to transfer a wafer to or from the processing chamber), the mainframe controller <b>110</b> detects the pressure change via the first pressure transducer <b>126</b> and accordingly adjusts one or both of the flow rate of the mass flow controller <b>112</b> and the position of the throttle valve <b>116</b>. The conventional system <b>100</b> thus employs a feedback control loop comprising the first pressure transducer <b>126</b>, the mainframe controller <b>110</b>, the mass flow controller <b>112</b> and the throttle valve <b>116</b> to maintain the desired pressure within the transfer chamber <b>102</b>.

0009To control the pressure in the first load lock <b>104</b> and the second load lock <b>106</b>, the conventional system <b>100</b> employs a separate vacuum pump <b>128</b> coupled to the first load lock <b>104</b> via a second isolation valve <b>130</b> and coupled to the second load lock <b>106</b> via a third isolation valve <b>132</b>. Both isolation valves <b>130</b>, <b>132</b> are controlled by pneumatic control signals from the mainframe controller <b>110</b> and may be individually opened/closed to selectively evacuate each load lock. Similarly, a regulated nitrogen flow may be provided to each load lock <b>104</b>, <b>106</b> via a regulated nitrogen supply <b>134</b> coupled to both the first load lock <b>104</b> and the second load lock <b>106</b> via an isolation valve <b>136</b> and an isolation valve <b>138</b>, respectively. The pressure within the first load lock <b>104</b> is measured by the mainframe controller <b>110</b> via a second pressure transducer <b>140</b> and the pressure within the second load lock <b>106</b> is measured by the mainframe controller <b>110</b> via a third pressure transducer <b>142</b>. Note that an isolation valve <b>144</b> that is controllable by the mainframe controller <b>110</b> also is provided between the regulated gas supply <b>114</b> and the filter <b>122</b> (e.g., so as to allow the mass flow controller <b>112</b> to be bypassed if desired).

0010The conventional system <b>100</b> of <figref idref="DRAWINGS">FIG. 1</figref> suffers from a number of drawbacks. For example, the mainframe controller <b>110</b>'s empirical calculation of both a flow rate for the mass flow controller <b>112</b> and a throttle valve position for the throttle valve <b>116</b> based on a measured pressure within the transfer chamber <b>102</b> is a complex calculation that (1) is not highly accurate (e.g., as the method by which a mass flow controller measures mass flow is prone to error unless repetitive calibration is used); and (2) may be time consuming to implement because the mainframe controller <b>110</b> may need to control numerous other functions (e.g., the operation of the first load lock <b>104</b>, of the second load lock <b>106</b>, of various processes and processing chambers (not shown) coupled to the transfer chamber <b>102</b>, etc.) and because of the slow response time of the throttle valve <b>116</b>. Accordingly, the pressure within the transfer chamber <b>102</b> is not highly regulated (e.g., may fluctuate to an unacceptable level for a given period of time). Additionally, the conventional system <b>100</b> is expensive because of the use of a throttle valve (e.g., the throttle valve <b>116</b>) and a mass flow controller (e.g., the mass flow controller <b>112</b>), and because of the use of a separate pump (e.g., the vacuum pump <b>128</b>) to control the pressure within first load lock <b>104</b> and the second load lock <b>106</b>.

0011Accordingly, a need exists for improved methods and apparatus for maintaining a pressure within a vacuum chamber such as a transfer chamber of a semiconductor device manufacturing tool.

SUMMARY OF THE INVENTION

0012In accordance with a first aspect of the invention, a system is provided for maintaining a pressure within a chamber such as a transfer chamber, a processing chamber or the like. The system includes (1) a chamber; (2) a variable speed vacuum pump coupled to the chamber; and (3) a pressure controller coupled to the chamber. The pressure controller is adapted to compare a set point pressure with a pressure measurement for the chamber and to adjust a flow of gas through the pressure controller based on a difference between the pressure measurement and the set point pressure.

0013The system also includes a pressure measurement device coupled to the chamber and to the pressure controller, and a main controller coupled to the variable speed vacuum pump, the pressure controller and the pressure measurement device. The pressure measurement device is adapted to measure a pressure within the chamber and to provide a pressure measurement to the pressure controller and/or to the main controller. The main controller is adapted to (1) adjust a speed of the variable speed vacuum pump; and (2) provide the set point pressure to the pressure controller.

0014In a second aspect of the invention, the chamber is a transfer chamber and the system includes a load lock and/or a processing chamber coupled to the transfer chamber. A single pump may pump both the transfer chamber and the load lock. Numerous other aspects are provided.

0015Other features and advantages of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

0016<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram of a conventional system for maintaining a pressure within a transfer chamber of a semiconductor device manufacturing tool;

0017<figref idref="DRAWINGS">FIG. 2</figref> is a block diagram of an exemplary inventive system for maintaining a pressure within a transfer chamber of a semiconductor device manufacturing tool;

0018<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram an alternative inventive system for maintaining a pressure within a transfer chamber of a semiconductor device manufacturing tool; and

0019<figref idref="DRAWINGS">FIG. 4</figref> is a top plan view of a semiconductor device manufacturing tool configured in accordance with the present invention.

DETAILED DESCRIPTION

0020To address the needs of the prior art an inventive system is provided for maintaining a pressure within a vacuum chamber (such as a transfer chamber, a processing chamber or the like). Specifically, <figref idref="DRAWINGS">FIG. 2</figref> is a block diagram of an exemplary inventive system <b>200</b> for maintaining a pressure within a transfer chamber of a semiconductor device manufacturing tool (e.g., the Endura™ (shown in <figref idref="DRAWINGS">FIG. 4</figref>) or the Centura™ (not shown), both manufactured by Applied Materials, Inc.). While the present invention is described below with reference to a transfer chamber of a semiconductor device manufacturing tool, it will be understood that the invention may be employed with any environmentally controlled chamber, whether the chamber is operated above, at or below atmospheric pressure.

0021For convenience, only the differences between the conventional system <b>100</b> of FIG. <b>1</b> and the inventive system <b>200</b> of <figref idref="DRAWINGS">FIG. 2</figref> are described herein, and like reference numbers are employed for components that perform similar functions. With reference to <figref idref="DRAWINGS">FIG. 2</figref>, the main differences between the conventional system <b>100</b> and the inventive system <b>200</b> are: <ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0022">1. the mass flow controller <b>112</b> is replaced with a pressure controller <b>202</b> and the output signal of the first pressure transducer <b>126</b> is fed to both the pressure controller <b>202</b> and the mainframe controller <b>110</b>;</li><li id="ul0002-0002" num="0023">2. the throttle valve <b>116</b> is not employed;</li><li id="ul0002-0003" num="0024">3. the vacuum pump <b>118</b> is replaced with a variable speed vacuum pump <b>204</b> that has a speed that may be controlled by the mainframe controller <b>110</b> (via a pump speed control signal); and</li><li id="ul0002-0004" num="0025">4. the vacuum pump <b>128</b> is not employed (e.g., the variable speed vacuum pump <b>204</b> is employed to pump the first load lock <b>104</b>, the second load lock <b>106</b> and the transfer chamber <b>102</b>).</li></ul></li></ul>

0026The pressure controller <b>202</b> may comprise, for example, a volumetric flow controller having a proportional integral derivative (PID) closed-loop control unit (e.g., an MKS Instruments Model No. MKS-640 pressure controller) that compares the output signal from the pressure transducer <b>126</b> to a set point pressure established by the mainframe controller <b>110</b> and that adjusts the volumetric flow rate of nitrogen into the transfer chamber <b>102</b> so as to maintain the set point pressure (as described below). Other suitable pressure controllers may include, for example, pressure controllers that employ neural networks, fuzzy logic, etc., for feedback control. Alternatively, the pressure controller <b>202</b> may comprise a flow controller such as a proportional valve that lacks feedback control, and the main controller <b>110</b> may adjust flow rate through the pressure controller <b>202</b> based on pressure measurements from the pressure transducer <b>126</b>. In either case, a particular advantage of employing a pressure controller rather than a mass flow controller is that unlike mass flow control, pressure control is independent of gas type.

0027The variable speed vacuum pump <b>204</b> may comprise any conventional pump (e.g., a mechanical pump) having a pump speed that may be varied (e.g., so as to allow a suction flow rate of the pump to be varied in accordance with variations in a motor speed of the pump). Conventional pumps that may modified (e.g., by varying the voltage that drives the pump motor based on the signal from the mainframe controller <b>110</b>) so as to have variable speed pump rates are well known in the art and include, for example, various mechanical pumps manufactured by Edwards, Alcatel, Ebara and the like.

0028With reference to <figref idref="DRAWINGS">FIG. 2</figref>, to employ the inventive system <b>200</b> to maintain a pressure within the transfer chamber <b>102</b>, a user (not shown) supplies the user defined input <b>108</b> to a mainframe controller <b>110</b> of the inventive system <b>200</b>. The user defined input <b>108</b> represents a pressure at which the transfer chamber <b>102</b> is to operate (e.g., a set point pressure for the transfer chamber <b>102</b>). To maintain the set point pressure within the transfer chamber <b>102</b>, the inventive system <b>200</b> employs the pressure controller <b>202</b> to adjust a volumetric flow rate of nitrogen (or some other inert, non-reactive gas supplied from a regulated gas supply <b>114</b>) into the transfer chamber <b>102</b> and employs the variable speed vacuum pump <b>204</b> to adjust a rate at which the nitrogen that flows into the transfer chamber <b>102</b> is pumped from the transfer chamber <b>102</b>. Other gases such as degassed oxygen also may be pumped from the transfer chamber <b>102</b>.

0029In general, the pump rate of the variable speed vacuum pump <b>204</b> serves as a gross pressure adjustment and is employed only when large pressure variations are detected or expected within the transfer chamber <b>102</b> (e.g., when a wafer is being transferred to or from the transfer chamber <b>102</b>, into or from one of the first load lock <b>104</b>, the second load lock <b>106</b> or a processing chamber (not shown)). Accordingly, after receiving the user defined input <b>108</b>, the mainframe controller <b>110</b> converts the user defined input <b>108</b> (typically a digital signal) into an analog set point pressure and supplies the analog set point pressure to the pressure controller <b>202</b>. The pressure controller <b>202</b> then employs a closed loop feedback control technique (e.g., a P, a PI or a PID control loop) to calculate a flow rate of nitrogen into the transfer chamber <b>102</b> that will establish the set point pressure.

0030The mainframe controller <b>110</b> also generates a pump speed control signal based on the set point pressure, and supplies the pump speed control signal to the variable speed vacuum pump <b>204</b> so as to set the variable speed vacuum pump <b>204</b>'s pump speed to a rate that will maintain the pressure within the transfer chamber <b>102</b> at a level that provides the pressure controller <b>202</b> maximum pressure range control. For example, if the pressure controller <b>202</b> has a flow rate range of 1 milliliter/minute to 1 liter/minute, the pump speed of the variable speed vacuum pump <b>204</b> may be set at a speed (e.g., an empirically determined speed) that allows the pressure controller <b>202</b> to control the maximum pressure variation within the transfer chamber <b>102</b> when the pressure controller <b>202</b> adjusts the flow rate of nitrogen from 1 milliliter/minute to 1 liter/minute. Note that the mainframe controller <b>110</b> also provides a pneumatic control signal to the first isolation valve <b>120</b> so as to open the first isolation valve <b>120</b> and allow nitrogen to flow from the regulated gas supply <b>114</b> through the pressure controller <b>202</b> and into the transfer chamber <b>102</b> via the nitrogen filter <b>122</b>. The mainframe controller <b>110</b> further provides a pneumatic control signal to the second isolation valve <b>124</b> so as to open the second isolation valve <b>124</b> and allow the vacuum pump <b>204</b> to pump the transfer chamber <b>102</b>.

0031After the pressure controller <b>202</b> establishes the flow rate within the pressure controller <b>202</b> and the mainframe controller <b>110</b> establishes the pump rate of the variable speed vacuum pump <b>204</b>, both the mainframe controller <b>110</b> and the pressure controller <b>202</b> employ the first pressure transducer <b>126</b> coupled to the transfer chamber <b>102</b> to monitor the pressure within the transfer chamber <b>102</b> (e.g., by periodically sampling the output signal of the first pressure transducer <b>126</b>). Based on each sampled output signal of the first pressure transducer <b>126</b>, the pressure controller <b>202</b> recalculates a flow rate of nitrogen to be flowed into the transfer chamber <b>102</b> so as to achieve the set point pressure. The mainframe controller <b>110</b> only adjusts the pump rate of the variable speed vacuum pump <b>204</b> if the pressure within the transfer chamber <b>102</b> cannot be sufficiently controlled via the pressure controller <b>202</b> (e.g., if a large positive pressure variation results so that the flow rate adjustment range of the pressure controller <b>202</b> is inadequate to efficiently reestablish the set point pressure).

0032When pressure variations result in the transfer chamber <b>102</b> (e.g., due to the opening of the first load lock <b>104</b> when a wafer is transferred into the transfer chamber <b>102</b> from the first load lock <b>104</b>, the opening of the second load lock <b>106</b> when a wafer is transferred out of the transfer chamber <b>102</b> to the second load lock <b>106</b>, and/or when a processing chamber (not shown) coupled to the transfer chamber <b>102</b> is opened to transfer a wafer to or from the processing chamber), the mainframe controller <b>110</b> and the pressure controller <b>202</b>, via the first pressure transducer <b>126</b>, detect the pressure change, and the pressure controller <b>202</b> adjusts the volumetric flow rate into the transfer chamber <b>102</b> accordingly. As stated, the mainframe controller <b>110</b> may choose to adjust the pump rate of the variable speed vacuum pump <b>204</b> to aid in rapid re-establishment of the set point pressure within the transfer chamber <b>102</b>. However, in general, the pump rate of the variable speed vacuum pump <b>204</b> may be held approximately constant.

0033The inventive system <b>200</b> thus employs a feedback control loop comprising the first pressure transducer <b>126</b>, the mainframe controller <b>110</b>, the pressure controller <b>202</b> and the variable speed vacuum pump <b>204</b> to maintain the desired pressure within the transfer chamber <b>102</b>. Because of the rapid response of the pressure controller <b>202</b> relative to the mainframe controller <b>110</b> and to the throttle valve <b>116</b> (FIG. <b>1</b>), the inventive system <b>200</b> may achieve a desired pressure within the transfer chamber <b>102</b> much more rapidly, and may maintain the desired pressure within the transfer chamber <b>102</b> to a much tighter tolerance, than the conventional system <b>100</b> of FIG. <b>1</b>.

0034To control the pressure in the first load lock <b>104</b> and the second load lock <b>106</b>, the inventive system <b>200</b> employs the same pump (e.g., the variable speed vacuum pump <b>204</b>) that is used to pump the transfer chamber <b>102</b>. Accordingly, because the inventive system <b>200</b> employs only a single pump and no throttle valve, the inventive system <b>200</b> is significantly less expensive than the conventional system <b>100</b> of FIG. <b>1</b>. If desired, a separate pump <b>302</b> (e.g., a non-variable speed pump) also may be employed with the inventive system <b>200</b> as shown in FIG. <b>3</b>.

0035In order to not adversely affect the wafer throughput of the system <b>200</b> due to the use of a single pump (FIG. <b>2</b>), software within the mainframe controller <b>110</b> may be configured to pump the first load lock <b>104</b>, the second load lock <b>106</b> and the transfer chamber <b>102</b> in a sequence. For example, when the system <b>200</b> of <figref idref="DRAWINGS">FIG. 2</figref> is first employed, the pump <b>204</b> may be used to pump the transfer chamber <b>102</b> to a base pressure, and the isolation valve <b>124</b> then may be closed. Assuming the transfer chamber <b>102</b> is primarily leak tight, the pressure within the transfer chamber <b>102</b> should not rise significantly and there should be no flow of gas into the chamber <b>102</b> from the pressure controller <b>202</b>. The pump <b>204</b> thereafter may be employed to evacuate one or both of the load locks <b>104</b>, <b>106</b> as required for substrate transfer. Likewise, the transfer chamber <b>102</b> may be pumped down to a base pressure after one or both of the load locks <b>104</b>, <b>106</b> have been evacuated.

0036In at least one embodiment, the vacuum pump <b>204</b> is an integrated point of use pump (IPUP) (e.g., a pump that is sufficiently small to allow the pump to be placed on a semiconductor device manufacturing tool so that the distance between the vacuum pump <b>204</b> and the isolation valve <b>124</b> is only about a foot as opposed to up to 100 yards when a conventional pump is employed). The use of an IPUP speeds up the response time on the suction flow rate side of the system <b>200</b> (e.g., the vacuum pump side of the system <b>200</b>) so that an adjustment to the pump speed of the vacuum pump <b>204</b> makes a rapid adjustment in suction flow rate. An IPUP also is less expensive than larger pumps, as is the cost of installing an IPUP (e.g., as only a short distance of plumbing is required). An example of an IPUP is the Alcatel ADP100L IPUP.

0037<figref idref="DRAWINGS">FIG. 4</figref> is a top plan view of a semiconductor device manufacturing tool <b>400</b> useful in describing the operation of the invention system <b>200</b> with a single pump such as an IPUP. Other tools or vacuum chambers may be similarly controlled.

0038With reference to <figref idref="DRAWINGS">FIGS. 2 and 4</figref>, in an exemplary operation, when a single pump is employed, the transfer chamber <b>102</b> may be connected to a shared IPUP <b>204</b> (<figref idref="DRAWINGS">FIG. 2</figref>) and a pressure controller <b>202</b> which is sized/configured for the correct operating pressure. The IPUP <b>204</b> may service the transfer chamber <b>102</b> and the load locks <b>104</b>, <b>106</b>. The base pressure for the transfer chamber <b>102</b> is set via the mainframe controller <b>110</b> (in response to a user-defined input <b>108</b>) and the transfer chamber isolation valve <b>124</b> is opened. Once the transfer chamber base pressure is reached, the transfer chamber isolation valve <b>124</b> is closed.

0039When a substrate is to be processed within the tool <b>400</b>, a substrate carrier <b>402</b> is loaded into one of the load locks <b>104</b>, <b>106</b> (load lock <b>104</b> in FIG. <b>4</b>). The load lock <b>104</b> then is exposed to the shared IPUP <b>204</b> (by opening isolation valve <b>136</b>) and is pumped down as required for substrate transfer (e.g., to the base pressure of the transfer chamber <b>102</b>). Both load locks <b>104</b>, <b>106</b> may be pumped simultaneously if desired.

0040Once the load lock <b>104</b> reaches the appropriate pressure, a slit valve <b>404</b> disposed between the transfer chamber <b>102</b> and the load lock <b>104</b> opens, and a substrate handler <b>406</b> located within the transfer chamber <b>102</b> extracts a substrate from the substrate carrier <b>402</b>. The substrate handler <b>406</b> retracts, and the slit valve <b>404</b> then may close. The pressure controller <b>202</b> responds to pressure fluctuations as required to maintain the transfer chamber base pressure.

0041Once the substrate is located within the transfer chamber <b>102</b>, the substrate may be similarly transferred to a processing chamber (such as a processing chamber <b>408</b>) or to a second transfer chamber <b>410</b>. For example purposes only, it is assumed that the substrate is to be transferred to the processing chamber <b>408</b>. Because the pressure within the transfer chamber <b>102</b> rises very slowly (e.g., assuming the transfer chamber <b>102</b> is primarily leak tight and/or does not outgas significantly), it is expected that the maximum allowable transfer chamber pressure will not be reached prior to the opening of a processing chamber slit valve <b>412</b> that separates the transfer chamber <b>102</b> and the processing chamber <b>408</b>. Accordingly, the pump <b>204</b> may be employed for other purposes (e.g., pumping load locks).

0042To transfer the substrate to the processing chamber <b>408</b>, the processing chamber slit valve <b>412</b> is opened. In response thereto, the pressure within the transfer chamber <b>102</b> decreases (due to pumping by a vacuum pump (not shown) coupled to the processing chamber <b>408</b>). The pressure controller <b>202</b> responds to this increased pumping speed/rate by flowing more nitrogen into the transfer chamber <b>102</b>. A pressure gradient thereby is generated from the transfer chamber <b>102</b> to the processing chamber <b>408</b> (e.g., allowing for processing gas abatement). The pressure gradient will be maintained as long as the maximum N₂flow is not reached. Note that in either a single pump configuration (<figref idref="DRAWINGS">FIG. 2</figref>) or a dual pump configuration (FIG. <b>3</b>), the pump connected to the transfer chamber <b>102</b> typically is isolated from the transfer chamber <b>102</b> before the processing chamber slit valve <b>412</b> is opened so that the processing chamber <b>408</b> is the only vacuum source (e.g., thereby maintaining the desired pressure gradient).

0043With the slit valve <b>412</b> open, the substrate handler <b>406</b> transfers the substrate from the transfer chamber <b>102</b> to the processing chamber <b>408</b> and retracts, and the processing chamber slit valve <b>412</b> closes. Once the processing chamber slit valve <b>412</b> is closed, the pressure controller <b>202</b> reduces (and/or shuts off) the N₂flow into the transfer chamber <b>102</b> (after the transfer chamber base pressure is reached). When the system is off-line or idle, the transfer chamber isolation valve <b>124</b> and the loadlock isolation valves <b>136</b>, <b>138</b> may remain open. The pressure controller <b>202</b> may continue to respond to pressure fluctuations to maintain the transfer chamber <b>102</b> and the load locks <b>104</b>, <b>106</b> at a desired off-line base pressure (if the slits valves between the transfer chamber <b>102</b> and the load locks <b>104</b>, <b>106</b> are open).

0044Note that the pressure inside a transfer chamber may be an important parameter during substrate transfers. For example, it may be desirable to maintain a pressure gradient between a processing chamber and the transfer chamber to induce a flow into the processing chamber when a slit valve of the processing chamber opens. This flow can serve as an inert gas purge for corrosion or explosion abatement. The flow can also reduce the amount of particles in the transfer chamber by flowing the particles into a less clean processing chamber and into a pump of the processing chamber. However, too large of a pressure differential between a processing chamber and the transfer chamber <b>102</b> may produce a large initial burst of gas into the processing chamber that stirs up contaminants within the processing chamber. One technique for avoiding such a gas burst is to limit the gain of the pressure controller <b>204</b>. The correct transfer chamber pressure can also improve the conductive and convective heat transfer from a hot substrate during substrate transfers.

0045An exemplary operating regime for pressure control within the transfer chamber <b>102</b> ranges from less than 1 T to near 100 T (where T=Torr). In such a range, there may be three pressure regimes: low, medium, and high pressure; and pressure changes due to the vacuum pump <b>204</b> and the nitrogen flow (from the pressure controller <b>202</b>) may be different within each pressure regime. For example, in the low pressure regime, below 1 T, the system <b>200</b> may run in a pump-limited mode where the response is slow if a negative pressure change is required. However, the pressure controller <b>202</b> may respond more quickly to a positive pressure change, such as from 100 mT to 1 T. Between 1 T and 10 T, or in the medium pressure regime, a higher N₂flow may have less of an influence on pressure because the vacuum pump <b>204</b> may be more efficient. Above 20 T, or in the high pressure regime, the vacuum pump <b>204</b> may be very efficient and have a large affect on pressure changes.

0046When designing a low pressure system, variables that may be taken into account include, for example, the internal volume of the transfer chamber <b>102</b>, the number of purge points, the nitrogen restrictions due to filters (e.g., the filter <b>122</b>) or other components, the nitrogen supply pressure, the range and position of the pressure transducer <b>126</b>, line size, and the size of the pressure controller <b>202</b>'s flow body. Other variables include pump speed, PID gain, and the like. Exemplary components include a 10 T Baratron pressure transducer <b>126</b> and a 1 slm pressure controller <b>202</b> with a proportional gain set to 4 and an integral gain set to 0. The vacuum pump <b>204</b> (e.g., an Alcatel ADP100L IPUP) may be run at its full speed, and a nitrogen pressure of 35 psi may be employed

0047When designing a high pressure system, a higher flow pressure controller <b>202</b> may be used in conjunction with pump speed control. One advantage of pump speed control is that a system with a slower pump speed may waste less nitrogen. In addition, the response time of the pressure controller <b>202</b> may be faster with a slower pump speed. The pump speed and the pressure controller P and I (for an MKS 640 pressure controller) may be set, for example, so that the pump speed is 30% of maximum, the P term is 3, and the I term is 1.

0048The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and method which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, other pressure ranges than those described above may be employed. The particular pressure controllers, pumps and other components described herein are merely exemplary. Other similar and/or suitable components may be employed. For example, a pressure measurement device such as an ion gauge, a residual gas analyzer or the like may be used in place of the pressure transducer <b>126</b>. While the present invention has been described primarily with reference to semiconductor device manufacturing, it will be understood that the invention may be applied to chambers used to process other types of substrates (e.g., glass substrates employed in flat panel displays), whether or not the chambers are operated above, at or below atmospheric pressure.

0049The mainframe controller <b>110</b> and/or any other controller may contain computer program code for performing any of the control functions described herein, and may include one or more inventive computer program products and/or data structures. Each computer program product may be carried by a medium readable by a computer (e.g., a carrier wave signal, a floppy disc, a compact disc, a DVD, a hard drive, a random access memory, etc.).

0050Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.